More than 50% of drugs on the market target G protein-coupled receptors (GPCRs). Among the most important of these are drugs used to treat neurological disorders, such as pain relievers, antidepressants and anti-psychotics, as well drugs used for neurodegenerative diseases such as Parkinson's disease and Alzheimer's disease. The relatively recent discovery of a family of proteins called "regulator of G protein signaling" (RGS), that attenuate GPCR signals by increasing the GTPase activity of associated Ga proteins, has opened up a new avenue for modulating the activity of endogenous and administered GPCR ligands. However, development of inhibitors to RGS proteins has been hampered by the lack of robust assay methods for high throughput screening (HTS). To overcome this technical hurdle, we propose to use fluorescence based immunodetection of GDP to measure RGS-dependent increases in the steady state GTPase activity of modified Ga proteins. Based on the approach used previously at BellBrook Labs for development of an ADP detection assay, a highly specific monoclonal antibody and fluorescent tracer will be developed for detection of GDP. The Ga proteins will be mutated to increase the rate of GDP dissociation relative to GTP hydrolysis so that the former is no longer rate limiting. The availability of these novel HTS assays will accelerate drug discovery focused on RGS proteins and delineation of their roles in GPCR signal transduction. Over half of current drugs exert their effects through a family of proteins called G protein- coupled receptors, and the targeting of these receptors has been especially useful for the development of drugs used to treat neurological disorders such as schizophrenia, depression, and Parkinson's disease. To accelerate discovery of more selective therapies for these and other diseases, we are developing novel screening assays for a family of proteins, called 'regulator of G-protein signaling' (RGS) that modulate the effects of GPCR ligands in a tissue-specific manner. [unreadable] [unreadable] [unreadable]